1. Field of the Invention
The present invention relates to a deformable structure employed in a cable support system for supporting a flexible cable. More particularly, the present invention relates to a deformable structure employed in a cable support system for supporting a cable on an industrial robot.
2. Description of the Related Art
A cable is extended along the outer surface of robot arms in an industrial robot (hereinafter referred to simply as “robot”). The cable has one end connected to an end effector and the other end connected to a peripheral device, such as a power unit. The cable includes bundles of wires for carrying power to the end effector and those for carrying command signals to the end effector and bundles of pipes for carrying working fluid necessary for operating the end effector. Parts of the cable are held by a plurality of clamping members attached to the robot.
When the shafts of the robot are displaced relative to each other by operating a wrist held on a robot arm at least for twisting, bending or turning, the distance between the clamping members attached to the adjacent shafts changes. Consequently, a part of the cable extending between the clamping members is bent and the cable is tightened or slackened. In some cases the cable is excessively slackened to collide against the peripheral device, or the cable is excessively tightened to be broken, if the shafts of the robot are displaced greatly
A cable support system capable of preventing the undesirable deformation of a cable is disclosed in Japanese Utility Model Laid-Open Publication No. 58-184293 (Patent document 1). This known cable support system is used on a driving apparatus having a stationary unit and a swivel unit capable of turning about a vertical axis. More specifically, a band-shaped member bent in a U-shape in a space is wound round the stationary unit and is attached to the stationary unit. Many support blocks having the shape of a rectangular pyramid are arranged densely on the curved inner surface of the band-shaped member. A cable is supported by the band-shaped member so as to wind loosely round the stationary unit. When the swivel unit turns through an angle relative to the stationary unit, the cable is deformed together with the band-shaped member in the vicinity of the axis of rotation. Thus the undesirable deformation of the cable is prevented.
A cable support system disclosed in Japanese Patent Laid-Open Publication No. 62-34795 employs chains instead of the band and the support blocks mentioned in Patent document 1. The chains form a passage having the shape of a circular arc for a cable. The adjacent chains can be turned through a predetermined angle relative to each other. This cable support system prevents the cable from being away from a driving apparatus.
Each of those known cable support systems disclosed in Patent documents 1 and 2 has a deformable cable support structure having the shape of a circular arc. The deformable cable support structure is wound round the driving apparatus. The deformable structure has a plurality of turnable segments arranged along the length thereof. Each turnable segment restrains the adjacent turnable segment from turning about an axis parallel to the axis of rotation and allows the adjacent turnable segment to turn about an axis perpendicular to the axis of rotation.
The cable support system disclosed in Patent document 1 needs a support ring for supporting the deformable structure thereon to prevent the deformation of the deformable structure by its own weight. The cable support system including the support ring is inevitably large. If the axis of rotation is horizontal, the deformable structure is unable to maintain a predetermined position and is unable to support a cable.
The deformable structure of the cable support system disclosed in Patent document 2 is formed by successively connecting a plurality of chain links with pins. The joint of the two chain links connected by the pin is loaded to maintain the deformable structure in a curved shape having a predetermined radius of curvature against the weight of the deformable structure. The two adjacent chain links connected by the joint need to be turnable relative to each other. The structural strength of the joint is low and the joint is subject to breakage. Therefore, the deformable structure cannot be formed in a large weight. The same problem arises when the axis of rotation is horizontal, a heavy cable is supported by the deformable structure, or a high acceleration is imparted to the deformable structure.